This section is intended to introduce the reader to aspects of art that may be related to various aspects of the present invention, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Engines having one or more rotational rotors are known to have numerous theoretical advantages over conventional engines utilizing linearly reciprocating pistons. Such advantages include smoother operation and improved engine balancing, fewer moving parts, lower frictional losses, and reduced size, weight, and cost. Most rotary engines also suffer, however, from one or more significant disadvantages which have severely limited their commercial acceptance. The type of rotary engine most commonly produced at this time utilizes an Otto cycle and an eccentric rotor, which significantly increases the complexity and manufacturing costs of the engine. Other rotary engines utilize a complex arrangement of planetary gears and cranks to operate connecting arms, multiple crankshafts, or sophisticated rhombic drives, thereby making the engine difficult to balance and expensive to manufacture.
Most engine designs are based directly on or are a slight variant of either the Ericsson cycle, the Stirling cycle, or the Otto cycle. An analysis of the thermodynamics of these engine cycles reveals that the Ericsson cycle theoretically provides the most work. The high volumetric displacement required for the constant pressure heating and cooling of this cycle, however, significantly increases the size of the engine and thus limits the practicality of utilizing this cycle for most applications.
The Otto cycle is well suited for engines in which combustion of a fuel occurs within an internal working chamber of the engine. The efficiency of the Otto cycle internal combustion engine is limited, however, by the temperature of the incoming gas. The efficiency of an engine utilizing the Otto cycle cannot, however, be continually increased by raising the temperature of the incoming gas, since gas temperature must be kept sufficiently low in order to prevent detonation (knocking) which severely detracts from engine performance.
The theoretical Stirling cycle achieves isothermal compression and expansion, with constant volume heating and cooling. This cycle has the advantage of theoretically increased efficiency over the Otto cycle, yet an engine utilizing this cycle does not require the substantially increased size and complexity of an Ericsson cycle engine. Rotary engines based upon the Stirling cycle seeking to combine the benefits of high efficiency for the Stirling cycle with the advantages of a rotary engine, utilize an offset axis for the rotor shaft and thus require displacer rotor vanes which move radially to maintain sealing integrity with the outer housing wall. The complexity, wear, and increased balancing problems created by this offset axis arrangement thus substantially detract from the previously disclosed benefits of a rotary engine.